5ffd1110e9
The region allocator marks freed regions "Condemned" before actually freeing them. Condemned regions are associated with a transaction; before they can be reused / coalesced the transaction that condemned them must complete. The region allocator used "TisActiveTransaction(xid)" to determine whether a given transaction had completed. The problem is that Stasis now reuses transaction id's, and condemned regions were never reclaimed in practice. A transaction fingerprint is a unique identifier (currently transaction id, rec_lsn) that can be used to distinguish transactions that did not execute concurrently. I considered an alternative design based upon end-of-transaction actions. This would have worked as well, but would have been a more invasive change.
74 lines
3.1 KiB
C
74 lines
3.1 KiB
C
#ifndef STASIS_OPERATIONS_REGIONS_H
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#define STASIS_OPERATIONS_REGIONS_H
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#include <stasis/operations.h>
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/**
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Allocates and deallocates regions of pages. The page before each
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region is of type BOUNDARY_TAG. All regions except the last one in
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the page file have a BOUNDARY_TAG page immediately after the end of
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the region.
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Each region is managed by an allocation manager, which manages the
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allocation of pages within a region. The contents of pages within
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a newly allocated region are undefined.
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*/
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typedef struct boundary_tag {
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pageid_t size;
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pageid_t prev_size;
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int status;
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stasis_transaction_fingerprint_t region_xid_fp;
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int allocation_manager;
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} boundary_tag;
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#define REGION_BASE (123)
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#define REGION_VACANT (REGION_BASE + 0)
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#define REGION_ZONED (REGION_BASE + 1)
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#define REGION_OCCUPIED (REGION_BASE + 2)
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#define REGION_CONDEMNED (REGION_BASE + 3)
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void regionsInit(stasis_log_t *log);
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pageid_t TregionAlloc(int xid, pageid_t pageCount, int allocaionManager);
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void TregionDealloc(int xid, pageid_t firstPage);
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pageid_t TregionSize(int xid, pageid_t firstPage);
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void TregionForce(int xid, pageid_t pid);
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/** Currently, this function is O(n) in the number of regions, so be careful! */
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void TregionFindNthActive(int xid, pageid_t n, pageid_t * firstPage, pageid_t * size);
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/**
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* Read the active boundary tag that follows the given region.
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* Inactive boundary tags (ones that are locked by ongoing transactions, or that point
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* to free space) will be skipped.
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*
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* @param xid The transaction reading the boundary tag
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* @param pid A pointer to the current pageid.
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* @param tag A pointer to a buffer that will hold the next boundary tag.
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* @param allocationManager The allocation manager whose tags should be returned, or 0 if all active tags should be returned.
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* @return 0 on failure, true on success
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*/
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int TregionNextBoundaryTag(int xid, pageid_t*pid, boundary_tag *tag, int allocationManager);
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/** Read the boundary tag marking the first page of some region. If pid = ROOT_RECORD.page, this will return the first boundary tag.
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*
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* @param xid The transaction examining the boundary tag
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* @param pid The first page in the region (ie: the one returned by TregionAlloc(). In the current implementation, the boundary tag lives on the page before this one.
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* @param tag A buffer that the tag will be read into.
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*/
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int TregionReadBoundaryTag(int xid, pageid_t pid, boundary_tag *tag);
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stasis_operation_impl stasis_op_impl_boundary_tag_alloc();
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stasis_operation_impl stasis_op_impl_region_alloc();
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stasis_operation_impl stasis_op_impl_region_alloc_inverse();
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stasis_operation_impl stasis_op_impl_region_dealloc();
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stasis_operation_impl stasis_op_impl_region_dealloc_inverse();
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/** This function checks the regions in the page file for consistency.
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It makes sure that the doublly linked list is consistent (eg
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this->next->prev == this), and it makes sure that all boundary
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tags pages (that are marked REGION_ZONED) occur somewhere in the
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linked list. */
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void fsckRegions(int xid);
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// XXX need callbacks to handle transaction commit/abort.
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#endif
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