LCStoreDB.php

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<?php
class LCStoreDB implements LCStore {

    private $currentLang;
    private $writesDone = false;
    private $dbw;
    private $batch = [];
    private $readOnly = false;

    public function get( $code, $key ) {
        if ( $this->writesDone && $this->dbw ) {
            $db = $this->dbw; // see the changes in finishWrite()
        } else {
            $db = wfGetDB( DB_SLAVE );
        }

        $value = $db->selectField(
            'l10n_cache',
            'lc_value',
            [ 'lc_lang' => $code, 'lc_key' => $key ],
            __METHOD__
        );

        return ( $value !== false ) ? unserialize( $db->decodeBlob( $value ) ) : null;
    }

    public function startWrite( $code ) {
        if ( $this->readOnly ) {
            return;
        } elseif ( !$code ) {
            throw new MWException( __METHOD__ . ": Invalid language \"$code\"" );
        }

        $this->dbw = wfGetDB( DB_MASTER );
        $this->readOnly = $this->dbw->isReadOnly();

        $this->currentLang = $code;
        $this->batch = [];
    }

    public function finishWrite() {
        if ( $this->readOnly ) {
            return;
        } elseif ( is_null( $this->currentLang ) ) {
            throw new MWException( __CLASS__ . ': must call startWrite() before finishWrite()' );
        }

        $this->dbw->startAtomic( __METHOD__ );
        try {
            $this->dbw->delete(
                'l10n_cache',
                [ 'lc_lang' => $this->currentLang ],
                __METHOD__
            );
            foreach ( array_chunk( $this->batch, 500 ) as $rows ) {
                $this->dbw->insert( 'l10n_cache', $rows, __METHOD__ );
            }
            $this->writesDone = true;
        } catch ( DBQueryError $e ) {
            if ( $this->dbw->wasReadOnlyError() ) {
                $this->readOnly = true; // just avoid site down time
            } else {
                throw $e;
            }
        }
        $this->dbw->endAtomic( __METHOD__ );

        $this->currentLang = null;
        $this->batch = [];
    }

    public function set( $key, $value ) {
        if ( $this->readOnly ) {
            return;
        } elseif ( is_null( $this->currentLang ) ) {
            throw new MWException( __CLASS__ . ': must call startWrite() before set()' );
        }

        $this->batch[] = [
            'lc_lang' => $this->currentLang,
            'lc_key' => $key,
            'lc_value' => $this->dbw->encodeBlob( serialize( $value ) )
        ];
    }

}